I think that a few pages (or chapters?) back its mentioned in the side notes that aestimare goes sometimes with genitive to specify how much."Mercatores merces suas magni aestimant, vitam nautarum parvi aestimant" for example.

So "Nonne liberos pluris aestimas quam merces istas" would be "do you not value children more than these merchandise?"

ēlūcet mâiōrem habēre vim ad discenda ista līberam cūriōsitātem quam meticulōsam necessitātemIt is clear that a free curiosity has a greater force in order to learn these things [languages] than a necessity based on fear. (St. Augustine, Cōnfessiōnēs I.14)